The large female staff, sometimes derisively referred to as a harem, consisted of women young and old. They were good at math, or devoted stargazers, or both. Some were alumnae of the newly founded women’s colleges, though others brought only a high school education and their own native ability. Even before they won the right to vote, several of them made contributions of such significance that their names gained honored places in the history of astronomy: Williamina Fleming, Antonia Maury, Henrietta Swan Leavitt, Annie Jump Cannon, and Cecilia Payne. This book is their story.
PART ONE
The Colors of Starlight
I swept around for comets about an hour, and then I amused myself with noticing the varieties of color. I wonder that I have so long been insensible to this charm in the skies, the tints of the different stars are so delicate in their variety. . . . What a pity that some of our manufacturers shouldn’t be able to steal the secret of dyestuffs from the stars.

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Glass plates are moved to new fireproof Brick Building Williamina Fleming prepares “A Field for Woman’s Work in Astronomy” for presentation at the Columbian Exposition in Chicago; discovers her first nova on plates from Arequipa Bruce telescope sees first light at Cambridge.
1895 Edward Pickering institutes the Harvard College Observatory Circular to describe news of the observatory, beginning with Williamina Fleming’s discovery of Nova Carinae (her second nova) from photographs taken at Arequipa; her third such discovery, Nova Centaurus, follows a few months later. Henrietta Swan Leavitt volunteers at the observatory Solon Bailey discovers many variables within certain star clusters of the Southern Hemisphere.
1896 Annie Jump Cannon joins the observatory as a research assistant, commences her study of the spectra of bright southern stars. Bruce telescope arrives at Arequipa.
1897 Antonia Maury publishes “The Spectra of Bright Stars” in the Annals, vol. 28, and is acknowledged as the author on the title page.
1898 National professional organization of astronomers, later named the Astronomical and Astrophysical Society of America, established at a meeting held at Harvard.

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Solon Bailey completes a provisional catalogue of 76 globular clusters in the Annals, vol. 76.
1918 First of nine volumes of the greatly expanded Henry Draper Catalogue is published in the Annals, beginning with vol. 91.
1919 Edward Pickering dies. Solon Bailey serves as interim director.
1920 Harlow Shapley and Heber Curtis debate the scale of the universe.
1921 Harlow Shapley is named fifth director. Henrietta Leavitt dies Harlow Shapley and Annie Cannon explore the relation between spectral type and magnitude.
1922 International Astronomical Union adopts Harvard’s Draper stellar classification, representing the work of Williamina Fleming, Antonia Maury, and especially Annie Jump Cannon.
1923 Adelaide Ames enrolls as Harvard’s first graduate student in astronomy. Cecilia Payne arrives from England as Harvard’s second graduate student in astronomy Harvard Reprints series initiated to disseminate staff members’ published articles in professional journals.
1924 Harlow Shapley issues the first in a series of papers detailing the distance, size, and structure of the Magellanic Clouds.

Resembling assembly-line workers in a factory, with their plain, unadorned dresses, these dedicated women—swiftly, accurately, and cheaply—numbered each star on a given plate, determined the star's exact position, and assigned it either a spectral class or photographic magnitude. Annie Jump Cannon, who established the stellar classification system adopted internationally in the course of this work, praised Pickering's modern outlook. “He treated [the computers] as equals in the astronomical world,” she claimed (somewhat Pollyannishly), “and his attitude toward them was as full of courtesy as if he were meeting them at a social gathering.” He was their gallant Victorian gentleman.
Pickering's first hire was his housekeeper, Williamina Fleming, who had displayed a keen intelligence in carrying out her duties. Frustrated one day by a male assistant's ineptitude, Pickering had declared that his maid could do a better job, and he found out she could.

(Roger Smith/NOAO/AURA/NSF/WIYN)
With the huge number of photographic plates of the northern and southern skies stacking up at the observatory on Garden Street in Cambridge, Massachusetts, Pickering shrewdly recognized the value of smart young women yearning to make contributions in an era that generally denied them full access to scientific institutions. Here was a ready workforce, he noted in one annual observatory report, entirely “capable of doing as much and as good routine work as astronomers who would receive much larger salaries. Three or four times as many assistants can thus be employed, and the work done correspondingly increased for a given expenditure.”
Williamina Fleming (standing) directs her “computers” while
Harvard Observatory director Edward Pickering looks on
(Harvard College Observatory)
These women “computers,” as they were called, many with college degrees in science, were situated in two cozy workrooms, pleasantly decorated with flowered wallpaper and star charts. Working at ma hogany writing tables, crammed together, each woman through the day might peer through a magnifying glass at her selected plate or industriously record her findings in a notebook.

But at least the women could now examine the photographic results of night-time observations and contribute to astronomy, a discipline that had largely excluded them in the past.
Figure 43 The Harvard ‘computers’ at work, busy examining photographic plates while Edward Pickering and Williamina Fleming watch over them. On the back wall are two plots that show the oscillating brightness of stars.
Although Williamina Fleming’s team of women computers were supposed to focus on the drudgery of harvesting data from the photographs so that the male astronomers could conduct the research, it was not long before they were reaching their own scientific conclusions. Endless days spent staring at the photographic plates had given them an intimate familiarity with the stellar objects that they were surveying.
For example, Annie Jump Cannon catalogued roughly 5,000 stars per month between 1911 and 1915, calculating the location, brightness and colour of each one.

…

He was still blocked from conducting military research, but within a few months his curfew was lifted and Baade had complete control of the world’s best telescope under ideal viewing conditions. He also made the most of the increasingly sensitive photographic plates that were becoming available, creating images of unparalleled sharpness.
Baade spent the war years studying a particular type of star known as an RR Lyrae star, a type of variable star similar to a Cepheid variable star. Williamina Fleming, who worked alongside Henrietta Leavitt at the Harvard Observatory, had shown that the variability of RR Lyrae stars could be used, like Cepheids, to measure distances. So far her technique had been used only within the Milky Way, because RR Lyrae stars are less luminous than Cepheids. However, Baade’s ambition was to use the ideal viewing conditions to find RR Lyrae stars in the Andromeda Galaxy, our nearest large galaxy.

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Bailey, History and Work of the Harvard Observatory 1839-1927 (McGraw Hill, 1931) An interesting and largely non-technical (if somewhat dry) account of the research projects pursued at the Harvard College Observatory from its founding until the mid-1920s. It covers the work of Henrietta Leavitt and Annie Jump Canon, and explains the techniques and instruments they employed.
Harry G. Lang, Silence of the Spheres (Greenwood Press, 1994) Subtitled The Deaf Experience in the History of Science, this book includes sections on John Goodricke and Henrietta Leavitt.
Edwin Powell Hubble, The Realm of the Nebulae (Yale University Press, 1982) A somewhat technical book, based on the 1935 Silliman Lectures delivered by Hubble at Yale University. It is an interesting snapshot of cosmology soon after Hubble’s major breakthroughs.

At Harvard College Observatory, a leader in the dull but promising business of stellar taxonomy, photographic plates that revealed the color and spectra of tens of thousands of stars were stacked in front of “computers”—spinsters, most of them, employed as staff members at a university where their sex barred them from attending classes or earning a degree. (Henrietta Leavitt, the pioneer researcher of the Cepheid variable stars that were to prove so useful to Shapley and Hubble, was a Harvard computer.) The computers were charged with examining the plates and entering the data in neat, Victorian script for compilation in tomes like the Henry Draper Catalog, named in honor of the astrophotographer and physician who had made the first photograph of the spectrum of a star. Like prisoners marking off the days on their cell walls, they tallied their progress in totals of stars cataloged; Antonia Maury, Draper’s niece, reckoned that she had indexed the spectra of over five hundred thousand stars. Theirs was authentically Baconian work, of the sort Newton and Darwin claimed to practice but seldom did, and the ladies took pride in it; as the Harvard computer Annie Jump Cannon affirmed, “Every fact is a valuable factor in the mighty whole.”3
It was Cannon who, in 1915, first began to discern the shape of that whole, when she found that most stars belonged to one of about a half-dozen distinct spectral classes.

…

If, for instance, we have two Cepheid variables with the same period, we may assume that they have about the same absolute magnitude. If the apparent magnitude of one is four times that of the other, we conclude (barring complications such as the interference of an intervening interstellar cloud) that the dimmer star is twice as far away.
The relationship between the periodicity and the absolute magnitude of Cepheid variable stars was discovered in 1912 by Henrietta Swan Leavitt, one of a number of women hired at meager wages to work as “computers” in the Harvard College Observatory office in Cambridge, Massachusetts. Leavitt spent her days examining photographic plates taken through the twenty-four-inch refracting telescope at the Harvard station in Arequipa, Peru. One of her tasks was to identify variable stars. This involved comparing thousands of pinpoint star images on plates taken on different dates, looking for changes in brightness.

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Noteworthy Events: Jacobus Kapteyn, studying the proper motions of twenty-four hundred stars, finds evidence of what he calls “star streaming”—that stars in our neighborhood move in a preferred direction—an early clue to the rotation of our galaxy.
Time: 1911
Noteworthy Events: Ernest Rutherford determines that most of the mass of atoms is contained in their tiny nuclei.
Time: 1912
Noteworthy Events: Henrietta Swan Leavitt discovers a correlation between the absolute magnitude and the period of variability of Cepheid variable stars, opening the door to their use as intergalactic distance indicators.
Time: 1913
Noteworthy Events: Niels Bohr develops theory of atomic structure, in which electrons are said to orbit the nucleus in a manner somewhat akin to that of planets orbiting the sun.
Noteworthy Events: Henry Norris Russell presents a plot of the luminosities and colors of stars, extending work done in 1911 by Ejnar Hertzsprung.

I was surprised how easy it was to roam at random without a hospital ID. I walked outside, where orderlies and other staff stood smoking cigarettes. I walked by the emergency room, where victims of knives, automobiles, and guns arrived in ambulances. I walked back up the steps to the surgical floor and sat again. I took out my laptop and tried to work on a book I was writing. It was about Henrietta Leavitt, the woman who in the early 1900s discovered the blinking stars astronomers use as beacons to measure the emptiness of the universe. She died, childless, of stomach cancer. Before long Nancy’s brother arrived. The earth had continued to rotate and it was dark outside. The cafeteria closed, and the lights were turned off. We were shooed into a hallway where a family—the only other visitors still on the floor—waited for the outcome of someone else’s long surgery.

…

Suppose you have two patients with the same kind of cancer. One responds to a drug and the other does not. Using a device like Hillis’s, you could take their proteomic snapshots and lay one on top of the other and look for something that is different. Even if you don’t know what the pattern means, it might be used as a marker to identify which patients will most likely benefit from the drug. I was reminded of Henrietta Leavitt, the astronomer who had died of stomach cancer but not before discovering Cepheid variables, the pulsating stars cosmologists use to measure the universe. She would start with two images of the same patch of sky—glass photographic plates taken a few weeks apart. One would be a negative with the stars glowing in black. She would place that plate on top of the other and hold the glass sandwich to the light.

Hubble's luck was to come along soon after an ingenious woman named Henrietta Swan Leavitt had figured out a way to do so. Leavitt worked at the Harvard College Observatory as a computer, as they were known. Computers spent their lives studying photographic plates of stars and making computations—hence the name. It was little more than drudgery by another name, but it was as close as women could get to real astronomy at Harvard—or indeed pretty much anywhere—in those days. The system, however unfair, did have certain unexpected benefits: it meant that half the finest minds available were directed to work that would otherwise have attracted little reflective attention, and it ensured that women ended up with an appreciation of the fine structure of the cosmos that often eluded their male counterparts.
One Harvard computer, Annie Jump Cannon, used her repetitive acquaintance with the stars to devise a system of stellar classifications so practical that it is still in use today.

They were first described in 1521 by the chronicler accompanying Magellan’s voyage of circumnavigation of the globe—so they are called the Large Magellanic Cloud and the Small Magellanic Cloud.
They were not studied in detail until John Herschel observed them from the astronomic observatory at the Cape of Good Hope in 1834 (the expedition that fueled the Moon Hoax). Like the Milky Way, the Magellanic Clouds turned out to be assemblages of vast numbers of very dim stars, dim because of their distance.
In the first decade of the twentieth century, the American astronomer Henrietta Swan Leavitt (1868–1921) studied certain variable stars in the Magellanic Clouds. By 1912, the use of these variable stars (called Cepheid variables because the first to be discovered was in the constellation Cepheus) made it possible to measure vast distances that could not be estimated in other ways.
The Large Magellanic Cloud turned out to be 170,000 light-years away and the Small Magellanic Cloud 200,000 light-years away.

What he saw changed humanity’s view of the universe forever—and would further roil the controversy over science’s role in defining the origins of creation. A conservative Baconian observer, Hubble photographed a small blinking star in the Andromeda nebula that he identified as a Cepheid variable. This observation would become iconic in its power.
Another astronomer, Harvard College Observatory’s Henrietta Leavitt, had in 1912 shown something remarkable about Cepheid variable stars: The longer their period, the brighter they appeared to be. This made sense. Stars were very faint, and to probe deeply, astronomers began to mount cameras to their telescopes and take very-long-exposure photographs on glass plates so they could capture light from stars that were too faint to see with the human eye. A blinking star that has a longer “on” period deposits more light on the plate than one with a shorter period.